Hello Nikolay Velizhanin,
There have been some changes in the RadPanelBar and now by design the PreviewCollapsed event occurs before the PreviewExpanded event(in order to expand an item you should collapse the other first). To get the sample project working you should use the Selected(or PreviewSelected) event instead of the PreviewExpanded event. I've updated the attached project, so could you please examine it and if you have further questions feel free to ask?
the Telerik team
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